Fix an uninitialized read of m_forceIntegerFacePoints reported by valgrind:

==32250== Conditional jump or move depends on uninitialised value(s)
==32250==    at 0x54B631: TrenchBroom::Model::FindFacePoints::instance(bool) (Face.cpp:34)
==32250==    by 0x54E1A3: TrenchBroom::Model::Face::updatePointsFromBoundary() (Face.cpp:488)
==32250==    by 0x54D31C: TrenchBroom::Model::Face::Face(TrenchBroom::VecMath::BBox<float> const&, bool, TrenchBroom::VecMath::Vec<float, 3ul> const&, TrenchBroom::VecMath::Vec<float, 3ul> const&, TrenchBroom::VecMath::Vec<float, 3ul> const&, std::string const&) (Face.cpp:361)
==32250==    by 0x4E2E6F: TrenchBroom::IO::MapParser::parseFace(TrenchBroom::VecMath::BBox<float> const&, bool) (MapParser.cpp:339)
==32250==    by 0x4E1C5F: TrenchBroom::IO::MapParser::parseBrush(TrenchBroom::VecMath::BBox<float> const&, bool, TrenchBroom::Utility::ProgressIndicator*) (MapParser.cpp:244)
==32250==    by 0x4E1606: TrenchBroom::IO::MapParser::parseEntity(TrenchBroom::VecMath::BBox<float> const&, TrenchBroom::IO::MapParser::FacePointFormat&, TrenchBroom::Utility::ProgressIndicator*) (MapParser.cpp:165)
==32250==    by 0x4E1A55: TrenchBroom::IO::MapParser::parseMap(TrenchBroom::Model::Map&, TrenchBroom::Utility::ProgressIndicator*) (MapParser.cpp:213)
==32250==    by 0x55731D: TrenchBroom::Model::MapDocument::loadMap(char*, char*, TrenchBroom::Utility::ProgressIndicator&) (MapDocument.cpp:136)
==32250==    by 0x556AE9: TrenchBroom::Model::MapDocument::DoOpenDocument(wxString const&) (MapDocument.cpp:79)
==32250==    by 0x727FBF: wxDocument::OnOpenDocument(wxString const&) (docview.cpp:417)
==32250==    by 0x55A325: TrenchBroom::Model::MapDocument::OnOpenDocument(wxString const&) (MapDocument.cpp:668)
==32250==    by 0x72C861: wxDocManager::CreateDocument(wxString const&, long) (docview.cpp:1522)
Merge pull request #930 from ericwa/uninitialized-read-fix

TB1: Fix an uninitialized read of m_forceIntegerFacePoints reported by valgrind